1. Field of the Invention
This invention relates to an electromagnetic relay, particularly to one having a moving contact for a low acoustic noise in operation for use in such as automobile, audio-system, or personal computers.
2. Description of the Related Art
With a recent increase in usage of an electromagnetic relay in many fields such as automobile, audio-system, or personal computers, it has been desired to decrease acoustic noise in the operation of an electromagnetic relay having a moving contact, particularly for use in such a place that a quiet environment is required. Thus, the need for a so-called silent relay has been increased. The acoustic noise is caused by impact sounds which are originally emitted when an iron core impacts an armature, and also a moving contact impacts a fixed contact. These sounds are propagated to the outside by air confined by an outer encapsulation and mechanical components of the relay. Several attempts have been made to prevent the impact sounds from coming out. FIG. 1 is a schematic cross sectional view of the first conventional low noise relay, in which a body of an electromagnetic relay 1 is enclosed by an air-tight double container consisting of an inner and outer containers 12, 11. The inner container 12 is separated by a buffer material 14 like sponge from the outer container 11. An inner terminal lead 13 penetrating a wall of the inner container 12 is connected to an outer terminal lead 15 also penetrating a wall of the outer container 11 by a flexible mesh wire 16. Therefore, an impact sound can be absorbed by the air-tight double container and a mechanical vibration can be damped by the buffer material and the flexible mesh wire. FIG. 2 is a perspective bottom view of a second conventional low noise relay, in which a body 2 of the electromagnetic relay is suspended by an inner base 21 arranged at a top of the body 2 with three folded terminal leads 22, 23, 24. Further, the folded terminal lead 22 and a moving contact spring 26 are fixed to a side wall of an electromagnet 27. The moving contact spring 26 having an armature 25 on the fixed end is arranged at a bottom of the body together with the armature 25, while a free end of the moving contact spring 26 vibrates between a pair of fixed contact springs 28, 29. Although a part of an operating sound is admitted to be emitted to the outside through an outer encapsulation (not shown), terminal leads 22, 23, and 24 can damp the vibration during propagation. FIG. 3 is an explosive view of the third conventional low noise relay, in which a buffer 41 is arranged between a body 3 of the electromagnetic relay and an outer base 4. The buffer comprises blade springs 43 having terminal leads 44 and insulating plate 42, which are unified by insert mold technique. The body 3 has an electromagnet 33 on an inner base 31 such that an axis of coil 32 is parallel to the outer base 4. The armature 34 is opposite to the electromagnet 33 by a moving contact spring 35. Further, a pair of parallel contact springs 36, 37 are fixed to the inner base 31 between which a free end of the moving contact spring 35 is arranged such that the free end of the moving contact spring 35 vibrates in parallel to the outer base 4 together with the armature 34 driven by the activated coil 32. Each of the electric lines connecting with the coil 32, a moving contact spring 35, and a pair of parallel contact springs 36, 37 are coupled with the corresponding inner terminal 38 which is not directly extended to the outside, but, instead, is connected with the corresponding blade spring 43 arranged around the periphery of the buffer 41, from which each of the terminal lead 44 is extended outside the outer base. Similarly as before, the impact noise can be decreased by absorbing the vibrational energy into the buffer 41. However, the first conventional low noise relay can not avoid elevating a temperature of the enclosed body due to heat generated by the activated coil and switching contacts during operation. Further, a complex structure of the double container prevents miniaturization and manufacturability of the relay, both of which are rather constant requirements for an advanced relay. The second conventional low noise relay has the armature and the moving contact spring which both vibrate in the direction parallel to the terminal leads suspending the body. Therefore, the vibrational energy propagates in the terminal leads by a longitudinal mode which can not be damped efficiently. The third conventional low noise relay has the armature and the moving contact spring which both vibrate in the direction parallel to the buffer 41, but the blade spring 43 has such a short length between a fixed point and a force-acting point that a vibrational energy can not be damped much against expectation. Consequently, any of the conventional low noise relays can not fully satisfy the requirements for use in a quiet environment.